1. Field of the Invention
The present invention relates to an oxygen absorbing compound mainly comprising an ascorbic acid compound which does not bring about any spontaneous ignition in the air and which is free from any danger of overheat ignition during its use. More specifically, it relates to an oxygen absorbing compound obtained by mixing the particles of a thermoplastic resin with an oxygen absorbing composition consisting principally of an ascorbic acid compound, and a method for culturing anaerobic bacteria by the use of this oxygen absorbing compound.
2. Description of the Related Art
Oxygen absorbing compounds mainly comprising ascorbic acid compounds are known as raw materials of oxygen absorber which are used in packages of foods for the purpose of protecting the foods from mold, oxidation and the like. As the oxygen absorbing compounds which can be used in the oxygen absorbers, there are well known the oxygen absorbing compounds mainly comprising iron powders in addition to the oxygen absorbing compounds mainly comprising the ascorbic acid compounds. In food making, a metal detector has been used sometimes to prevent metallic matters such as needles from getting into the food packages, and the oxygen absorbers mainly comprising the iron powders are sensed by the metal detector. Therefore, they cannot be applied to such a use, and hence, in this case, the oxygen absorber mainly comprising the ascorbic acid compounds can be employed. The oxygen absorbers mainly comprising the ascorbic acid compounds emit a carbon dioxide gas substantially as much as the volume of absorbed oxygen, so that the volume of each package does not change. Thus, in the fields of the foods and the like in which the appearance change of each package due to the decrease in the gas volume in the package by the absorption of oxygen is unrecommendable, the oxygen absorbers mainly comprising the ascorbic acid compounds have been used. Furthermore, in medical institutions, the food makers and the like, the culture inspection of anaerobic bacteria has been carried out for the purpose of the inspection of disease-causing bacteria, food poisoning bacteria and food contaminating bacteria, but in order to culture the anaerobic bacteria, it is necessary that oxygen should be eliminated from a culture environment in a short period of time and the environment containing a carbon dioxide gas should be prepared. The oxygen absorbing compounds mainly comprising the ascorbic acid compounds are filled into packages having an excellent breathability, and they are used as gas concentration adjustors for the culture of the anaerobic bacteria.
The oxygen absorbing compound using the ascorbic acid compound can be obtained by mixing the ascorbic acid compound, an alkali powder, a metallic salt, water and an activated carbon, as disclosed in Japanese Patent Application Laid-open Nos. 136845/1976, 10884/1977, 98348/1979, 132246/1979 and 61914/1980. In addition, in Japanese Patent Application Laid-open Nos. 105288/1979 and 51890/1983, methods for culturing the anaerobic bacteria have been disclosed in which a carbon dioxide gas emitting performance of the oxygen absorbing compound using the ascorbic acid compound is utilized.
The oxygen absorbing compound mainly comprising the ascorbic acid compound absorbs oxygen in an oxidative reaction of the ascorbic acid compound, and therefore, heat is generated during this reaction. With the aid of the generated heat, the reaction is further accelerated, whereby the oxygen absorption can be achieved in a short period of time. However, the ascorbic acid compound which can be used as the principal ingredient is an organic compound which is combustible, and an activated carbon which is mixed with the ascorbic acid compound is also a combustible material designated in fire regulations (coals and charcoals). Therefore, when a large amount of the oxygen absorbing compound absorbs oxygen, when gas concentration adjustors prepared by filling the oxygen absorbing compound into breathable small bags are accumulated in large quantities and they absorb oxygen, or when the oxygen absorption is done at a high atmospheric temperature even in the presence of a small amount of the oxygen absorbing compound, the generation of the reaction heat increases, and as a result, there is a fear that the combustible components in the oxygen absorbing composition may spontaneously ignite. Accordingly, this kind of oxygen absorbing compound is required to be sufficiently carefully handled in consideration of the danger of the spontaneous ignition during storage, use, disposal and the like.
In addition, a technique of controlling the overheat of the oxygen absorbing compound is also known. For example, Japanese Patent Application Laid-open No. 269376/1993 has disclosed a method in which an inorganic filler is used as a carrier to inhibit the danger of the spontaneous ignition. However, in the case that the inorganic filler is used as the carrier, a large amount of the heat is absorbed by the inorganic filler, so that the sufficient generation of the heat does not occur and the progress of the oxygen absorbing reaction retards. Therefore, there is a drawback that a large amount of the oxygen absorber is required in order to complete the oxygen absorption in a short time.
Moreover, Japanese Patent Application Laid-open No. 188288/1991 has disclosed a method which comprises adding a thermally meltable additive to a rust preventive mainly comprising an unsaturated fatty acid to inhibit the overheat. However, since the rust preventive does not generate any carbon dioxide gas and emits a bad odor, it cannot be used as the oxygen absorbing compound which can be used in the gas concentration adjustor for the culture of the anaerobic bacteria and the oxygen absorber for foods.